Don't prune variable-depth children while a minzoom-gated feature is pending
The minzoom_feature_pending flag from #397 keeps a variable-depth pyramid
subdividing until explicit per-feature minzooms are satisfied, but two gaps
let features still be dropped:
The flag was only set when tippecanoe_minzoom > z + 1, so a feature whose
minzoom is exactly z + 1 never marked the tile pending, even though a leaf
at z carries only z-visible content.
The early-stop commit never consulted the flag: a tile that succeeded in
stopping early inserted itself into skip_children_out unconditionally,
pruning the children the pending feature needed. The flag only inflated
estimated_complexity_out, which the pruning ignores.
Set the flag for any feature excluded below its minzoom, include it in the
early-stop veto, and skip child pruning while it is set. Adds a fixture
covering the minzoom == z + 1 boundary; make test passes with no diffs to
existing fixtures.
--generate-variable-depth-tile-pyramid decides a tile is a leaf once its
geometry fits at full detail, then prunes the tile's entire subtree. The
guard that prevents leafing while deeper content is still pending consults
only feature_minzoom (the automatic dot-dropping zoom); it does not consult
tippecanoe_minzoom, the explicit per-feature minzoom set via the
tippecanoe.minzoom attribute.
So a feature carrying an explicit minzoom deeper than where its region leafs
is excluded from the leaf tile (z < minzoom) while its children are never
generated. It ends up in no tile at any zoom, silently dropped.
next_feature() excludes such a feature and continues without returning it,
so the leaf-prevention guard in write_tile() never sees it. Carry a flag out
of next_feature() when an excluded feature first appears beyond the next
zoom, and feed it into the same estimated-complexity path feature_minzoom
already uses, so the pyramid keeps subdividing down to the feature's minzoom.
The flag only affects estimated_complexity_out, which is written solely under
--generate-variable-depth-tile-pyramid, so builds without that flag are
unchanged. make test passes with no fixture diffs.
Brandon Keepers